The present invention relates to a facsimile system and more particularly to a facsimile system suitable for effecting subscanning using a motor, with improvement of the subscanning which is reinitiated after the suspension of read scanning or record scanning.
A conventional facsimile apparatus is constructed as shown in FIG. 1 (a) and FIG. 1 (b). Referring to FIG. 1 (a), image element data DI for each line, which are fed from a scanner 1, followed by a synchronizing pulse PI, are temporarily stored in a buffer apparatus 2. Then, in accordance with a data requesting pulse Po from a data compression apparatus 3, data Do for one line are applied from the buffer apparatus 2 to the data compression apparatus 3. The data compression apparatus 3 codes the data Do for one line accordance with the run length and when the thus coded data Do do not reach a predetermined number of bits, supplementary bits are added thereto by the data compression apparatus 3, whereby the data compression operation for one line is completed. When the data compression operation for one line has been completed, a pulse Po requesting the data for the next one line is applied to the buffer apparatus 2 and, at the same time, the compressed data are transmitted to the reception side through MODEM 4.
On the other hand, on the reception side, as shown in FIG. 1 (b), the data transmitted from the transmission side through MODEM 5 are fed to a data expansion apparatus 6, where the coded data are decoded in the form of original image element data D'I which are then stored in a buffer apparatus 7 line by line. Awaiting the accumulation of the image element data D'I in the buffer apparatus 7, a plotter 8 picks up the image element data D'I for one line from the buffer apparatus 7 and records the same.
Thus, an original sheet set on the transmission side is read by the scanner 1 and the read data are transmitted to the reception side, where the transmitted data are reproduced, by the plotter 8, on a recording paper set on the reception side. When compressed data are transmitted from the transmission side to the reception side, the data transmission time for one line is always set longer than the read and record time for one line in order to increase the transmission efficiency and to reduce the number of the necessary buffers on the reception side and to simplify the construction of the facisimile system.
The subscanning for effecting the read scanning and record scanning is performed using motors, particularly pulse motors 9 and 10, respectively. In other words, when the buffer apparatus 2 on the transmission side becomes empty, the pulse motor 9 is driven in accordance with the synchronizing pulse PI and the image element data DI for one line are read by the scanner 1, while moving the original sheet in the subscanning direction. On the reception side, when the image element data D'I for one line are accumulated in the buffer apparatus 7 and it becomes possible to pick up the image element data D'I therefrom, the pulse motor 10 is driven in accordance with a synchronizing pulse P'I and image element data D'I for one line are recorded by the plotter 8, while moving the recording paper in the subscanning direction.
Therefore, when the images of the original sheet are complicated and the number of bits of the compressed data for one line are great, a long time is required for the transmission processing and there is a waiting time for the read scanning and the record scanning. As a result, the read subscanning and the record subscanning are performed intermittently, so that the pulse motors 9 and 10 are frequently started and stopped in repetition.
Furthermore, as shown in FIG. 2, when the read scanning or record scanning for one line is completed at a time To and the next scanning is suspended, even if the application of the subscanning pulse to the pulse motors 9 and 10 is stopped, the motors 9 and 10 do not stop immediately and the hunting thereof occurs, since the pulse motors 9 and 10 have their own inertia, respectively.
When the read scanning or record scanning for the next line becomes possible during this hunting period of .tau., and the pulse motors 9 and 10 are started, the linearity of the subscanning is damaged so that uneven scanning is caused. Particularly when the scanning resumption period falls on a hunting period .tau.1 of the motors 9 and 10, the scanning position greatly deviates from a desired scanning position, so that a satisfactory image is not reproduced on the reception side.
In the conventional facsimile apparatus, the buffer apparatuses 2 and 7 are provided with buffers for three lines, to which the image element data are fed and from which the image element data are picked up line by line, whereby the reading and recording and transmission processing are also conducted line by line.
Therefore, the scanning suspending period .tau.s from the suspension of the read scanning or record scanning through the resumption of the scanning becomes shorter than the hunting period .tau. and a case frequently occurs where the next scanning is initiated while the hunting of the motors is taking place. This does not permit formation of good recording images.
To be more specific, on the transmission side, as shown in FIG. 3, the image element data DI1, DI2, and DI3 for each line are successively stored in the buffers A, B, and C of the buffer apparatus 2, respectively, as shown in FIG. 3 (b), in accordance with the synchronizing pulses PI1, PI2 and PI3 of FIG. 3 (a) from the scanner 1. When the image element data DI1, DI2 and DI3 for the three lines have been stored in the buffer apparatus 2, image element data DI4 of the fourth line cannot be fed to the buffer apparatus 2 until the buffer A becomes empty, so that the read scanning is suspended. When a data requesting pulse Po1 is produced from the data compression apparatus 3 as shown in FIG. 3 (c), the data Do1 of the buffer A are picked up by the data compression apparatus 3 as shown in FIG. 3 (d). When the run length coding of the image element data Do1 is effected successively and the data Do1 of the first line does not reach a predetermined number of bits and the transmission time for the one line does not reach a predetermined transmission time, the data compression apparatus 3 adds supplementary bits to the dtat Do1 of the first line to make the data Do1 a code having bits more than the predetermined number of bits for one line and feeds the data Do1 to the MODEM 4 and applies the next data requesting pulse Po2 to the buffer apparatus 2 when the coding has been completed. As a result, when the buffer A becomes empty, it becomes possible to store data in the buffer apparatus 2 from the scanner 1, so that the read scanning is resumed by the next synchronizing pulse PI5.
However, the transmission processing time for the stored image element data Do1 of the first line is short and there is only time .tau. equivalent to one line scanning time as the scanning suspension period from the completion of the read scanning of input image element data DI3 of the third line through the initiation of the read scanning of the next fourth line. Therefore, the period of resuming the read scanning falls on the reverse hunting period, .tau.1, so that the subscanning cannot be performed properly and desired image element data cannot be obtained as the data for the DI4 of the fourth line.
Furthermore, for the originals which tolerate low scanning line density, generally the transmission processing is performed, with the scanning line density reduced to 1/2, in order to increase the transmission efficiency per original sheet.
When this method is adopted in the conventional facsimile system, the read scanning and recording scanning speeds have to be made greater than the data transmission speed and accordingly the subscanning speed has to be doubled. In this case, the main scanning speed is usually doubled, but it does not necessarily follow that the main scanning speed has to be doubled. In particular, this applies to the scanner side. If only the subscanning is made rough on the reception side, the space between dots which form characters is broadened. This results in the characters appearing lightly printed. Therefore, the main scanning speed is generally doubled and writing is performed twice.
Therefore, the hunting period and amplitude of the motor are increased when the scanning is suspended, so that the linearity of the subscanning at the time of initiation of the scanning is further lowered in comparison with the case where the scanning line density is 1. Accordingly image quality if further lowered.
For the above-mentioned reasons, conventionally, a measure is taken to meet the situation at the time of resumption of the scanning by the use of a motor capable of producing a large torque. However, motors having large torques produce much noise when starting and generate much heat. Furthermore, in the conventional facsimile system, when the scanning line density is made rough, the frequency of the scanning pulse has to be changed in order to make the subscanning speed high, which requires complicated circuits.